Mount Prospect, Illinois 7 Day Weather Forecast

Wx Forecast - Wx Discussion - Wx Aviation

520
FXUS63 KLOT 231922
AFDLOT

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
222 PM CDT Sat May 23 2026

.KEY MESSAGES...

- Scattered showers and isolated storms are possible this
  evening through Sunday morning, with the greatest chances of
  thunderstorms around and west of I-39 this evening and east
  of I-55 Sunday morning.

- Above normal temperatures are expected through early next
  week, though cooler conditions will occur near Lake Michigan
  each day.

&&

.DISCUSSION...
Issued at 222 PM CDT Sat May 23 2026

An upper-level low over southern Manitoba will shift NNE
through tonight as a trough axis extending from the Arrowhead of
Minnesota to the Missouri River Valley drifts eastward.
Meanwhile, an ongoing occlusion of the associated low-level warm
sector is ongoing across eastern Iowa into southwest Wisconsin.

As low-level moisture increases via advection across western
Illinois (evident in the low 60s dew points and growing cumulus
early this afternoon), a scattered to broken axis of showers
with some embedded thunderstorms is expected to develop later
this afternoon over eastern Iowa and drift eastward across
eastern Illinois into this evening. Coverage of thunderstorms
remains questionable as modest mid-level warming should inhibit
deeper surface-based convection through sunset. Additionally,
weak flow of under 25 knots throughout the potential convective
layer would yield short-lived, slow-moving cells. That said,
decent low-level CAPE below the mid-level warming indicates
showers could produce locally heavy rain even in the absence of
thunder through this evening. Expectation is for the highest
chances to reside around and west of I-39 very late this
afternoon into mid-evening before shower and storm chances wane
with eastward extent late this evening into the early overnight
hours.

Continued low-level moisture advection ahead of the slow-moving
front tonight will then interact with a trio of forcing
mechanisms to increase shower coverage generally around and east
of I-55 late tonight and especially from sunrise to mid-morning
Sunday. Coverage may increase quickly as loosely coupled upper
jet streaks align with a secondary mid-level trough axis and
mid-level convectively enhanced wave currently emanating from
Oklahoma. Thunder chances again appear relatively low, but with
PWATs increasing to over 1.5 inches and the bulk of CAPE
supportive of low-centroid cells, efficient precip and swaths of
heavy rainfall appear likely. Also cannot rule out brief
funnels under any growing convection over the far southeast CWA
mid-morning as surface-based instability increases, though the
best chance appears over southern IL/IN closer to more favored
surface vorticity.

High pressure will then bring quieter conditions to the area
late Sunday through Memorial Day and possibly through Tuesday.
An attempt at Rex blocking is becoming more evident in guidance
mid to late week as ridging over the central and northern Great
Plains is undercut by a southwestern trough cutting off over
Texas and the Lower Mississippi Valley. Expansive Hudson Bay
high pressure Tuesday and Wednesday will drift southward across
the Great Lakes region late in the week, which should stave off
higher precip chances during this period. Between these windows
above, a backdoor front associated with the approaching wave may
bring a period of showers and some storms to the area Wednesday
before precip clears south by Thursday.

Kluber

&&

.AVIATION /18Z TAFS THROUGH 00Z MONDAY/...
Issued at 110 PM CDT Sat May 23 2026

Key Messages:

- Scattered showers will likely pass through the area tonight
  into tomorrow morning. A few isolated lightning strikes may
  also occur (~20% chance).

- Easterly wind shifts from lake breezes are expected at the
  Chicago metro terminals this afternoon and again tomorrow.


Skies have cleared out quite a bit from earlier, but the
expectation is for VFR cloud cover to increase in coverage once
again this evening as a somewhat diffuse frontal zone slides
through the area. Scattered showers are expected to be present
across this frontal zone as it shuffles its way eastward and
could briefly knock flight categories back down to MVFR if they
end up passing directly over the terminals tonight. A few
isolated lightning strikes may also occur with this activity
(roughly a 20% chance of occurring near any particular TAF
site). Earlier on in the evening, these showers may also
produce gusty winds at RFD with the chances for gusty winds
then decreasing with time as the showers move into the Chicago
metro.

A lake breeze will also progress inland this afternoon, shifting
winds to a more easterly direction behind it (more northeasterly
at GYY). Winds will become light and variable tonight before
adopting a north-northwesterly direction after sunrise tomorrow.
Another lake breeze will push inland later on in the day and
result in another easterly wind shift at the Chicago metro
terminals, though confidence in the precise timing of this wind
shift remains low at this time.

Ogorek

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.

&&

$$

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